Assessment of lysyl oxidase variants by urea gel electrophoresis: Evidence against disulfide isomers as bases of the enzyme heterogeneity

Methods for the copurification and rapid assessment of the protein profiles corresponding to the multiple variants of bovine aortic lysyl oxidase are described. The individual variants do not resolve from each other by electrophoresis in sodium dodecyl sulfate but are resolved by gel electrophoresis in 8 m urea, thus providing a new method for their detection independent of enzyme assay. Alkylation of the purified mixture of the variants with iodoacetamide after reduction with dithiothreitol identified three disulfides per 32,000-Da monomer. Urea gel electrophoresis revealed that the heterogeneity of lysyl oxidase persists after reduction and alkylation, indicating that disulfide isomers are not the bases of the enzyme heterogeneity.